1. Field of the Invention
The present invention relates to a method for drilling, completing, producing, fracturing and stimulating a gas and/or oil well using a hydrocarbon fluid compositions having improved foaming properties, improved gas retention properties, and improved pumping properties. The invention also relates to methods for making the compositions and to compositions.
More particularly, the present invention relates to a method for producing a stable, hydrocarbon drilling fluid foam, where the method includes the step of pumping a pre-gasified, foamable hydrocarbon drilling fluid into a drilling string and/or a borehole of a well during drilling operations. As the fluid passes through a drill bit at the end of the drill string and into the well, the fluid changes from a pre-gasified, foamable hydrocarbon drilling fluid into a stable hydrocarbon drilling foam resulting in a decrease in column weight of the fluid in and an increase in a withdrawal rate of the drilling fluid and/or cutting from the well. After the stable hydrocarbon drilling foam exits the well, the foam defoamed or broken using a defoamer. The defoamed hydrocarbon drilling fluid is then refoamed with or without the addition of a refoaming additive or additional foamer. The present invention also relates to other uses of the compositions of this invention. The present invention also relates to a drilling fluid composition including a hydrocarbon fluid, a viscosifying composition, optionally a foaming agent and optionally a gas and, especially to a pre-gasified, foamable hydrocarbon fluid.
2. Description of the Related Art
In oil and gas drilling operations, it has been the almost universal practice up until recent years to circulate a liquid, such as water, oil, a water-in-oil emulsion, or an oil-in-water emulsion, usually with mud solids, clay particles, suspended therein, to and from the drilling zone during the drilling operation. One of the functions in circulating these drilling fluids, usually in the form of a drilling mud, is to remove drilled solids from the bit and lift cuttings from the bore. As can be readily understood the drilling liquid must be circulated under high pressure to assure entrainment of cuttings and expulsion of mud from the bore hole.
In recent years, some wells have been successfully drilled at a reduced pressure by a different technique in which a compressed gas, such as air, nitrogen or mixtures thereof, is pumped into the well along with drilling fluid at the drilling site. Cryogenic nitrogen (99.9999% N2) and membrane nitrogen (>93% N2) are the most common gases used since they are provide a safer drilling environment since hydrocarbons particularly natural gas can be flammable in gas environments possessing great than 7% oxygen content. This technique is called underbalanced drilling or managed pressure drilling. The compressed gas flows rapidly up the well bore annulus around the drill collar carrying with it the drilled solids and thus removing them from the drill hole. While in some instances, the drilling operation is essentially a dry process in many formations, water high in electrolyte concentration, enters the bore hole from adjacent water-containing strata. Such water invasion most often occurs while drilling in or through a water bearing subterranean zone, but may also be encountered in any area in the vicinity of trapped underground water.
Some of the advantages of the underbalanced or managed pressure drilling method over the more conventional mud drilling method include increased penetration rate, longer bit life, accurate location of water-bearing zones and measurement of flow, precise location of oil and gas bearing zones, especially those of low formation pressure, flow and pressure testing of productive zones without resort to drill stem tests, a lessening of possible contamination of prospective or known producing zones known as formation damage, and greater flexibility in physical-chemical alteration of the drilling fluid to meet particular down hole conditions such as adjusting the fluid density by changing the gas to liquid ratio. However, one difficulty in under-balanced or managed drilling where water seeps into the bore and accumulates in the drilling zone is that the drilled solids tend to agglomerate as the drill string rotates. These agglomerated masses become too heavy to be lifted out by gas alone which leads to many drilling problem such as stick drill pipe. As a result, rheology modifiers or thickeners must be used to suspend the drill cutting. Cutting suspension in under-balanced or manage pressure drilling typically is achieved with foaming agents.
In recent years, the technology of air and mud drilling has been combined in an attempt to provide drilling foams which have greater lifting strength than air but which do not have the pressure limitations of drilling muds.
The rheological properties of aqueous foams are of great importance for a number of applications in petroleum production. These properties include high flow rates in tubes or pipes and in porous media such as oil-bearing sandstones. Aqueous foam has advantages in oil fields that contain viscous oil in low pressure reservoirs. In these operations, the foam raises to the surface not only sand pulverized by the bit but also pebbles and rocks of considerable size.
The requirements for utilization of an aqueous foam in subterranean formations include high stability with waters containing appreciable quantities of soluble salts, such as sodium chloride, potassium chloride, calcium salts and/or magnesium salts, iron salts, and the capability for handling a variety of foam breaking elements such as crude oil and solids. Further the foam must not degrade under extremes of physical environments.
Numerous foam compositions have been proposed and used under such conditions, however most have proven unsatisfactory in one respect or another. Among the various classes of foaming compositions are nonionics; however, these are affected by salts and high temperatures encountered in drilling. Although many anionic surfactants provide acceptable foams in soft waters, they form foam breaking precipitates in the presence of brine and/or hard water. Cationics and zwitterionics are ineffective foamers because of their intolerance to high salinity. Foams used with hydrocarbon based drilling fluids such as diesel or kerosene based drilling fluids are difficult to foam and if foamed, are difficult to maintain for time sufficient for circulation through the well.
To our knowledge, there is no single-phase oil base foam drilling fluid on the market. However, many current drilling operations are using two-phase systems, in which air or nitrogen is injected into crude oil or diesel without the addition of chemical. Also, many drilling fluids use emulsified oil and CaCl2 brine to achieve a low density drilling fluid. However, many of these types of systems are used in conventional, over-balanced drilling. The potential problem with a two-phase drilling fluid is once the pump rate decreases gas begins to migrate out of the fluid. As the gas migrates out of the fluid, the drilling fluid begins to lose viscosity especially “low-end” or thixtropic viscosity, which is critical for hole-cleaning. As a result, a cutting bed is established which is attributed to several drilling problem like differential sticking.
By drilling with a stable single-phase system, the problems associated with hole cleaning due to loss of viscosity is greatly reduced. Thus, there is a need in the art for oil-based drilling fluids that are capable of producing a stable oil-based drilling fluid foam.